BTW, on the original "The.... " question, my feeling is that it's got quite a lot to do with patrician colonial attitudes among the sorts of people who used to discuss foreign climes the most: diplomats, civil servants, politicians and foreign media correspondents.
My instinct is that the use of the "The... " construction was/is done - whether consciously or subconsciously - to subtly imply a form of superiority over "lesser" nations and cultures. Outside of the courtly states of Europe, most of the rest of the world was (in the eyes of these sorts of people, right into the middle of the 20th century), inhabited by peoples who ranged from simply inferior (in terms of education, culture, manners and so on) to savages. I think that part of this - as some have alluded to before - was to (again subtly) separate the geographical region from its inhabitants/culture/economy (since these latter elemets were considered secondary).
Thus one talked of going to "The Argentine" (to steal its silver, probably...), and by using that term one was (again, whether consciously or not) excluding the more esoteric aspects of that area - its people, its culture etc. Indeed, one would need to refer to "The people of the Argentine" in order to refer to the inhabitants - the term "Argentinian" automatically implies citizens of a nation state (with all the attendant connotations of sovereignty, autonomy, etc).
I wouldn't mind betting that a sociologist or social historian somewhere has done some academic work on this subject. In a spare few hours, I might try to have a look around. But I truly do think that there are deeper, sociological reasons why the "The... " construction was so common in reference to further-flung regions of the world.